1. Field of the Invention
The present invention relates to the field of liquid crystal displaying, and in particular to a direct backlight module.
2. The Related Arts
Liquid crystal display (LCD) has a variety of advantages, such as compact device size, low power consumption, and being free of radiation, and is thus widely used. Most of the LCDs that are currently available in the market are backlighting LCDs, which comprise a liquid crystal panel and a backlight module. The working principle of the liquid crystal panel is that liquid crystal molecules are interposed between two parallel glass substrates and a plurality of vertical and horizontal fine electrical wires is arranged between the two glass substrates, whereby the liquid crystal molecules are controlled to change direction by application of electricity in order to refract light emitting from the backlight module for generating images. Since the liquid crystal panel itself does not emit light, light must be provided by the backlight module in order to normally display images. Thus, the backlight module is one of the key components of an LCD. The backlight module can be classified as two types, namely side-edge backlight module and direct backlight module, according to the position where light gets incident. The direct backlight module arranges a light source, such as a cold cathode fluorescent lamp (CCFL) or a light-emitting diode (LED) at the back side of the liquid crystal panel to form a planar light source that directly provides lighting to the liquid crystal panel.
Referring to FIG. 1, a conventional direct backlight module comprises a backplane 100, LED light bars 200 arranged inside the backplane 100, a reflector plate 300 arranged inside the backplane 100, a light guide plate 300 disposed on the bottom reflector plate 200, a diffusion plate 400 arranged above the reflector plate 300, an optic film assembly 500 disposed on the diffusion plate 400, and a plastic frame 600 mounted to the backplane 100. The LED light bars 200 supply lights that are mixed in a backlighting chamber 150 defined by the backplane 100 and the diffusion plate 400 and are subjected to homogenization by the diffusion plate 400 and the optic film assembly 500 so that the LED light bars 200 that are seemingly like spot light sources are converted to a planar light source.
However, the light exit surface 202 of each LED light bar 200 is set in parallel to a light incident surface 402 of the diffusion plate 400. This makes the available light mixing distance constrained by the thickness of the backlight module so that homogenization of planar lighting and size thinning cannot be achieved simultaneously.